Diamond high pressure cell



May 5,1910 Rum 3,509,597-

DIAMOND HIGHBEssuRE `CELL Filed Jam `2, 1968 United States Patent O 3,509,597 DIAMOND HIGH PRESSURE CELL Robert S. Kirk, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 2, 1968, Ser. No. 694,917 Int. Cl. B29c 3/00 ABSTRACT OF THE DISCLOSURE An improvement is described in high pressure optical cells which employ diamond anvils for exerting very high pressures to specimens disposed therebetween whereby the specimen and phase change(s) brought about therein are visible during actual pressure application. The improved structure enables the use of inexpensive transparent natural unpolished diamond crystals in combination with inexpensive back-up means for supporting the opposed diamond crystals over the entire area of the face thereof opposite the juxtaposed faces, which apply pressure to the specimen. The back-up means for the diamonds are also transparent being of ordinary polished plate glass, such as a soda-lime or borosilicate glass.

BACKGROUND OF THE INVENTION The instant invention is an improvement over the high pressure optical cell disclosed in U.S. Patent 3,079,505- Weir et al. wherein two modified gem-cut type II diamonds, each weighing 0.036 gram, comprise the anvil elements. The culets of each diamond must be ground off to form small at surfaces, which may be disposed parallel to each other with the specimen placed therebetween. The holder for each diamond is bored out conically to permit the introduction of maximum infrared radiation flux to and through the diamond to the specimen. Diamonds fulfilling the criteria recited in U.S. 3,079,505 are not very common and such crystals are, therefore, even more expensive in large size than type I crystals of comparable size.

iIn practice, the substance to be studied, in the form of a fine powder, is inserted between the small at surfaces formed by grinding olf the culets of the aforementioned diamonds and, after assemblying the balance of the cell, load can be applied to the diamond anvils such that tremendous forces are exerted between the juxtaposed diamond surfaces and are, therefore, applied in turn to the powdered substance. In performing spectrum analyses, `while the substance being studied is subjected to selected high pressures, the cell, which will have been positioned in the focal point region of a conventional beam-condensing unit, will be scanned by the beam over some preselected spectrum. The rays passing through the diamond cell and pressurized specimen are received by suitable instrumentation, such as a spectroscope for analysis.

In order to apply force to the rear of each diamond and still maintain an open line of sight through the diamond cell, pressure is applied over only a small portion of the area of 'the rear face of the diamond, pressure transmission to the `diamond being by means of a hollow holder coming in contact therewith over a ring-like area. Such a load application, of course, subjects each diamond crystal to unnecessarily severe strains. High quality, polished, relatively large diamonds specifically contoured are required for such a structure and great care must be taken in use of the apparatus, because a broken diamond anvil will make for very costly experimentation.

In contrast to the aforementioned construction, the instant invention combines the high compressive strength and precise dimensions of two materials readily available 3,509,597 Patented May 5, 1970 lCe without need for expensive preparation thereof; namely, natural diamond crystals and polished plate glass. By using these materials a diamond high pressure cell has been constructed that is so inexpensive that one may consider making a new cell for each experiment. The cell allows samples to be subjected to pressures in the 50 kilobar and higher range, While observations may be made optically or by spectrum analysis of the specimen under pressure.

SUMMARY OF THE INVENTION In accordance with the instant invention the diamond high pressure cell preferably comprises two natural unpolished diamond crystals, which have smooth surfaces and are free from inclusions (when observed under X-SO magnification), these crystals being compressed together as anvils between transparent plate glass surfaces, which fully support and exert pressure against the entire rear face of the diamond crystal anvils.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will appear more clearly from the following detailed description of the preferred embodiment thereof made with reference to the drawings in which:

FIG. l is an elevational View partially in cross-section, of a conventional pressure applying device fitted with a high pressure cell as disclosed in U.S. 3,079,505;

FIG. 2 is a portion of the device of FIG. 1 in which the prior art high pressure cell has been replaced by the high pressure cell of the instant invention; and

FIG. 3 is an exploded view showing the diamond anvils and back-up support therefor for the high pressure cell of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference characters designated like or corresponding parts throughout the several views, there is shown in FIG. 1 a prior art diamond anvil cell assembly in place in a conventional pressure applying structure 10. Casing 11 of structure 10 is preferably composed of cold-rolled steel and may, for example, be about 1" thick, 3 inches wide and 6 inches long, a size suitable for mounting in a conventional beam condensing unit (not shown). Spindle 12 threadingly inserts into a bushing in the upper portion of casing 11. A calibrated spring 13 is positioned concentric about the spindle 12, spring 13A abutting a head 14 integral with said spindle at one end thereof and abutting annular collar 16 at the other end. Projecting to the side from collar 16 are stub shafts 17a, 17b, only one of which is shown. Pressure plate 18 is positioned adjacent to the opposite surface of casing 11 and the stub shafts 17a, 17'b are interconnected with pressure plate 18 by a lever arrangement on each side of casing 11 whereby the arms 19, 21 are pivotally connected to the sides of casing 11. The location of the pivot points are selected to provide proportional lengths productive of desired pressure ranges in combination with compression spring 13.

The pressure plate 18 bears against a first diamond holder 22, plate 18 being bored out to permit passage therethrough of the convergent cone of irradiation, which is to pass through holders 22, 23, respectively. Bearing 24 inserts into a bushing 26 in the lower portion of cas ing 11, the first and second diamond holders 22, 23 being positioned in back-to-back relationship within bearing 24 and being free to slide therein and be urged against shoulder 27 formed in bearing 24.

In operation pressure plate 18 is perpendicular to the diamond anvils 31, 32. This ensures the absence of components of force at right angles to the thrust axis and ern contourishown, the culets normally present at the p of such a coniguration must be ground oil to form nall ats 31a, 32a, parallel to surfaces 3112, 32h, respec-` vely. Diamond anvils 31, 32 are seated in recesses 33, 4 respectively with ats 31a, 32a in juxtaposition pro- :cting `beyond opposed surfaces 36, 37 of holders 22, 23, espectively. Rubber rings 38, 39 may be used to permit lignment of the diamond anvils under pressure. Operattg pressure is applied over aring-like area to face 31h y the bottom of recess 33; similar pressure is generated ver a ring-like area between face 32b and the bottom f recess 34. In this manner a centrally-located area of ach of faces 31h, 32h is open for the transmissionot adiant energy to andfrorn the `specimen (not shown) zhich would be located between faces 31a, 32a;

The load imposed during operation is determined by measuring `the compression of spring 1,3 and the pressures re calculated, by dividing the load exerted by plate 18 y the area of the smaller of the two faces 31a, 32a which each have an area of about `0.002` in. or less). By singndiamond` anvils with smaller/area faces 31a, 32a, .igher pressures can be generated in the `specimen using he `same basic equipment. `The improved diamond `pressure cellof `the instant inquire gem `quality stones` weighing about 0.2 carat (costing upwards `of $100 wholesale `for typed). Still further,

for spectrum analysis, which is` themain concern inthe i `Weir et. al. patent, type -II diamonds are required. Type 1I diamonds in sizes as large as 0.2 carat are most uncommon so Vthat the cost would be (more than` double: the `cost of type l diamonds of equivalent welght.

In the size diamond required in the instant invention` both type rII octahedra and type 1I macles are plentiful and are not at a premium. If the radiation source is in the ultraviolet region the construction described herein requires only that type Il'diamond anvils be used in cornbination with 100% silica `plate glass, sometimes referred to as quartz glass, in place of the regular plate glass backn up discs. On thecontrary, if infared radiation at wave-` lengths up `to 3.5 microns is employed for the spectrum analysis, the type 'Il diamond anvils would be provided with 100% silica plate glass, and for longer wave length infrared radiation it would be necessary to resort to other backup materials known to exhibit transparency to longer wave lengths. Even this requirement does `not increase `the cost of` the diamond cell of `this `invention to the point that it cannot readily be considered a disposable item for i octahedraV measuring about one millimeter across` are` compressed together (with a specimen ylocated therebea 'ention recognizes` for the ,iirst time that `the `unaltered v i urfaces of small and inexpensive `naturally.,occurring diaf nond crystals can beiperfect enoughfor use as diamond tnvils. Suchdiamond crystals (both type l and typell) .re generallytoo small to be mounted in holders such tween) along their1l1"directions- Theseopposed da` mond crystals 41, 42 (asshown in FIGS. 2 and 3) are forcedtogether by pressure applied tobacltupplugs, 43,

"44., 45 of Pyrex plate glass (81%` SiO2`, 13% B203, s

3.6% Na20,` 0.2% K2() and 2.2% A1203). Rings/46 and 47 are usually employedin the case of;` octahedra `diamonds in order to aidin'proper crystal orientation. How-r `ever,..these rings, whichimaybe made ofpolytetralluoroethylene, are not essential.

is arefound` in conventional apparatus, because it would )e impossible to retain suicicnt freely observable area or optical viewing or spectrum` analysis. Any useful neans for supporting `these small `diamonds alsovwould rave to be inexpensive soas not to dilute the' benetitsprol fidedby the above discovery. Iustsuchasupport means` las been found. This support means is (altransparent,

The octahedra, whichoccur as natural crystals .and do not require alteration for use as anvils, weigh about 0.01 carat.

The perfection of the crystal surfaces in naturally` occurring` diamond octahedra crystals and theeasilyob.

` `tainable plate; giassiplugs with `paralleloptically. true sur` 1b) readily available with parallel optically truesurfaces,

jc) able to withstand highlyconcentratedload applica` ,y

ions and stillprovide effectiveopticalftransmissien even n regions of highest stress gradients and (d) able to fully n area therebetween is smaller thanfthe r,contact areasbe-` support the rear `face of each ofthe smallopposed diai nond` anvils. This material is common plate glass, par- .icularly borosilicate plate glass. Plate glass in ordinary Jarlance means rolled `sheetsof glass (or drawn sheets i )f glass) ground and polished on `both sides to plane iurfaces, opticallyrtrue; Such, for example, is the matetial oflwhich plate glass mirrors are made. `The glass :omposition maybe those knownfas sodaflime, soda-lime-` silica, lead, borosilicate,f96% silica or 100% zfusedsilica. i

Even though, at` higher pressures (over 40 kilobars):

:racks develop in these `glass back-updiscs in the region i of highest stress gradient, asmay be expected, in the polished plate glassidiscs of `thickness in excess of figg for borosilicate glassorabout /s for otherplateglasses faces rpermit the cell `to be assembledsimply and with out `the `need for guiding or "polishing of its components; The` `only `alignment offthe diamonds which is required` is, to` orient the juxtaposed diamond faces 41a and 42a relative to each other by rotation such ithat the contact tweenface 41!) and glass plug 43 and between face 42h `and glass plug44. The crystaldisposition shown in FIG@ 3 represents a 60 rotation. ln this way, pressures may be tolerated between the diamond crystals that are higher such vcracks do `not propagate far enoughlintothe glass back-up `discs tot impair `the support `capabilitiesthereof` and they are soinexpensive that they can be readily replaced with new `glass discs for future experiments. These bacloup discs are easily prepared by merely cutting round plugs from a larger plate glass sheet.

One method of comparing the instant invention `with the arrangement disclosed in Weir et al. is by comparing the size and cost of the diamondk anvils employed. In the instant invention octahedra `of industrial quality weighing about 0.01 carat (costing about $.50 each at wholesale prices) or macles (twin diamond crystals) of industrial quality weighing about 0.1 carat (costing about $5.00 each at wholesale prices) are used. Weir et al. re-

`thanthe pressures betweenthe diamondsfand the glass. With the massiversupportuof the glass backup plates, the practicallirnit of the pressure rbetween, diamond anvils easily exceeds 45 kilobars.

`Ina modified version providing the best compromise` of convenience and cost, the cell maybe constructed em`` ploying a natural diamond macle and a singleoctahedron. Preferably the macle (about 0:1 carat)selected is some-` what `larger than thatofthe opposing `octahedron (about i 0.01 carat) in which case the problem of positioningtbe samplebetween the `diarnondsis greatly simpliled and rings 46, 47 may` readily be eliminated. i If desired, still another modification may be employe wherein one cut and polished `.diamond 'of the configuration shown in US. 3,079,505 having a flat about 0.5 millimeter across is employed in combinationwith a diamond macle larger in face area than the area of the flat. Numerous tests have shown that most failures of the diamond anvils in this type of high pressure kcell occur in that diamond anvil face having the larger surface. Therefore, the use of macles which are very inexpensive restricts breakage if it should occur, to the inexpensive macle, rather than to the cut and polished anvil. 

